1. Field of the Invention
The present invention relates generally to a process for internally and externally upsetting the ends of a metal tube to form a drill pipe, particularly where the tube is used to form a section of upset horizontal directional drilling drill pipe.
2. Description of the Prior Art
Metal tubes which are used to form drill pipe of the type under consideration may have tube ends which are externally upset, internally upset, or both externally and internally upset, depending upon the end application. There are important differences in this regard, between traditional oil field drill pipe and the so-called “horizontal directional drilling” (HDD) drill pipe. Today, most oil field drill pipe is both internally and externally upset, for example to obtain the thickest possible wall for welding to a tool joint. Horizontal Directional Drilling (HDD) drill pipe is typically shorter and of smaller diameter than oil field drill pipe. Also, in the case of HDD drill pipe, the ends may be machined directly, without welding on a tool joint. As s result, the upset region of the HDD drill pipe tends to be relatively long, as compared to the upset region of oil field drill pipe. For example, a typical section of traditional HDD drill pipe might be approximately ten feet long with a pin end that is relatively long compared to the overall length of the section of pipe, for example, approximately 9 inches long.
There are two main processes for upset forging of metal tubes in general, the mechanical, impact process, and the hydraulic upset forging process. The impact process is accomplished by heating the end of the tubes, with an impact punch being used to form the upset on the pipe end. In the case of a drill pipe, the upset region is then threaded to produce a finished product. This process has been used for many years in both the oil field and the HDD industries. However, a chief limitation of the impact process for producing HDD product is that the method is restricted to relatively large internal diameter tubes because of the impact nature of the process used in making the upset. The smaller diameter tubes tend to break the impact punch and cause other problems. These limitations have kept HDD drill pipe manufacturers from being able to thread certain of the smaller internal diameter OEM thread designs, such as the Ditch Witch™ or the common IF™ thread.
The other process for upset forging of metal tubes uses a slow, consistent hydraulic pressure to form the upset. So called “closed die”forging machines are known which are hydraulically actuated to open and close dies and to provide the forging forces. Large hydraulic pumping capacities are typically required, since the dies must move through a substantial distance between the closed position and the open position in which finished parts are removed and subsequent blanks are inserted for subsequent working. While the closed die forging method has found use in a number of industries in forging metal parts, this method has not, to Applicant's knowledge, previously been used in the HDD pipe industry.
The present invention has as one object to overcome certain of the deficiencies noted with respect to the use of the impact forging method in forming HDD drill pipe with upset ends.
Another object of the invention is to adapt a closed die forging method to the manufacture of HDD product, the HDD product having a relatively smaller internal diameter in the threaded upset region than has previously been achievable with the impact forging process.